1. Field of the Invention
This invention relates to detectors, and more particularly, to pressure detectors.
2. Description of Related Art
Most modern electronic elements, such as integrated circuits, transistors, diodes, thin-film transistors for liquid crystal display driving circuits, and solar cells, are made by using inorganic silicon. Since the substrate and active region of these electronic elements are composed of silicon, the substrate of these electronic elements are rigid and difficult to bend, not working normally when rolled or folded.
Since deposition of organic material may take place at or near room temperature, if the inorganic silicon of the active region (channel layer) of elements in the electronic elements is replaced with an organic semiconductor material, the substrate of the electronic elements can be a flexible plastic substrate or a metal sheet. Such electronic elements are called flexible electronics.
The flexible electronics are defined as those electronic element products that are fabricated on a flexible substrate (for example, a plastic substrate or a metal sheet), and have a variety of characteristics, such as flexibility, low fabrication temperature and light-weight construction. Flexible electronics may be deposited on a plastic substrate, and may operate normally when bent and rolled. Flexible electronics have the advantages of being rollable, portable, and disposable, and can be fabricated in large sizes.
However, there are still some bottlenecks and problems in the application and development of the organic electronic elements and flexible pressure detectors and/or arrays and/or touch panels of flexible electronics.
Taiwanese Patent Application No. 200532854, “Organic vertical transistor and the fabrication method thereof,” discloses how to fabricate an organic vertical transistor having a source/drain/gate and teaches the operation mechanism whereby an active layer of an organic semiconductor is controlled by the gate in a way similar to that of an ordinary organic field-effect transistor. However, the organic vertical transistor operates at high voltage and lacks a pressure-detecting function.
U.S. Pat. No. 7,002,176, “Vertical Organic Transistor,” discloses a vertical organic transistor that is applicable to organic electronic elements only, and thus lacks a pressure-detecting function.
U.S. Pat. No. 5,191,237, “Field-Effect Transistor Type Semiconductor Sensor,” discloses a field-effect transistor sensor that not only functions as a sensor but also changes variable resistance according to applied pressure and allows voltage to be applied to the gate of the field-effect transistor so as to modulate the current of the drain. Therefore, the amplitude of the external pressure may be estimated by the amplitude of the current of the drain. However, the field-effect transistor sensor of U.S. Pat. No. 5,191,237 comprises an ordinary inorganic field-effect transistor and thus cannot be fabricated on a flexible substrate for use in flexible electronics. The sensor is still an ordinary field-effect transistor, and does not belong to the art of organic electronic elements of flexible electronics and flexible pressure detectors.
U.S. Pat. No. 7,112,755, “Pressure-Sensitive Sensor,” discloses a pressure sensor. The pressure sensor comprises a thin film configured to function as a pressure-sensing layer and formed from a mixture of plastic/rubber and conductive particles. However, electrodes of the pressure sensor are disposed between upper and lower substrates and comprise a plurality of upper electrodes and a lower electrode to thereby disadvantageously prevent miniaturization of the pressure sensor. The lower substrate of the pressure sensor is not an electrode, and thus the pressure sensor has limited application and cannot combine with organic electronic elements.
U.S. Pat. No. 7,260,999, “Force Sensing Membrane,” discloses a pressure-sensing membrane, which is fabricated by using two electrodes that are crossed to each other in an passive way. However, leakage currents are generated between each small pressure unit. Therefore, the pressure sensing membrane has limited application and cannot combine with organic electronic elements.
U.S. Pat. No. 7,141,839, “Organic Semiconductor Sensor Device,” discloses an organic sensor device, which uses an ordinary organic field-effect transistor as a pressure detector, wherein an organic layer is a sensing layer. However, the organic material is easily affected by external moisture and oxygen which can change the characteristics of the elements. The organic sensor device comprises an organic field-effect transistor and thus has to operate at high voltage to the detriment of standby time in practice.
“Pressure Sensing by Flexible, Organic, Field-effect Transistors,” Applied Physics Letter, Volume 89, 143502 (2006), a non-patent document, discloses a flexible organic field-effect transistor. However, it still belongs to an art in which an ordinary organic field-effect transistor is used as a pressure sensor. The organic material is easily affected by external moisture and oxygen, which can change the characteristics of the elements. The flexible organic field-effect transistor comprises an organic field-effect transistor and thus has to operate at high voltage to the detriment of standby time in practice.
“Organic-Transistor-Based Flexible Pressure Sensors Using Ink-Jet-Printed Electrodes and Gate Dielectric Layers”, Applied Physics Letters, Volume 89, 253507 (2006), another non-patent document, discloses an organic-transistor-based flexible pressure sensor, which uses an ordinary organic field-effect transistor in an array that has a designated position. However, in that the smallest unit of the whole area of the pressure sensor is the area that an organic field-effect transistor actually occupies, it is difficult to reduce the area of the pressure sensor. Moreover, the organic-transistor-based flexible pressure sensor, which comprises an organic field-effect transistor, needs to operate at high voltage to the detriment of standby time in practice.
Therefore, it is highly desirable to develop a flexible electronic element that may be fabricated on a flexible substrate, perform as a pressure detector and/or array and/or touch panel of flexible electronics, has the characteristics and functions of organic electronic elements and flexible detectors, and is capable of solving the drawbacks of the prior art, the drawbacks being that the organic detecting layer is readily affected by the surroundings, the organic field-effect transistor has too high of an operating voltage, and the size of the element area cannot be reduced.